US 7590388 B2 Abstract A method and arrangement for noise variance and SIR estimation in a UTRAN Node B or User Equipment estimates the SIR (SIR
^{(l) }. . . SIR^{(K)}) at the output of a detector by using an estimate ({circumflex over (σ)}^{2}) of the detector input noise variance to provide an estimate ({circumflex over (σ)}_{z} ^{2}) of the detector output noise variance. The detector input noise variance is derived from a midamble portion in the received signal. By deriving the transfer function of the detector an estimate of the detector output noise variance is estimated. The estimated output noise variance then allows an improved estimate of the SIR (SIR^{(l) }. . . SIR^{(K)}) at the detected output.Claims(32) 1. A method for noise variance estimation of a detected signal, the method comprising:
receiving a wireless signal and producing, from an input of the received wireless signal to a detector, a detected signal, wherein the detected signal is an output from the detector;
producing, from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
producing, from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
2. The method of
3. The method of
4. The method of
producing from the second noise variance signal and an estimate of total power at the detector output a signal-to-interference ratio (SIR) signal representative of SIR in the received wireless signal.
5. The method of
6. The method of
7. The method of
8. The method of
9. A user equipment capable of noise variance estimation of a detected signal, the user equipment comprising:
a detector for receiving a wireless signal and outputting from an input of the received wireless signal, a detected signal;
first noise variance logic for producing, from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
second noise variance logic for producing, from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
10. The user equipment of
11. The user equipment of
12. The user equipment of
signal-to-interference ratio (SIR) estimation logic for producing from the second noise variance signal and an estimate of total power at the detector output an SIR signal representative of SIR in the received wireless signal.
13. The user equipment of
14. The user equipment of
15. The user equipment of
16. The user equipment of
17. A base station capable of noise variance estimation of a detected signal, the base station comprising:
a detector for receiving a wireless signal and outputting, from an input of the received wireless signal, a detected signal;
first noise variance logic for producing, from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
second noise variance logic for producing, from the detected signal and the first noise variance signal a second noise variance signal representative of noise variance estimation of the detector in the received signal.
18. The base station of
19. The base station of
20. The base station of
SIR estimation logic for producing from second noise variance signal and an estimate of total power at the detector output an SIR signal representative of SIR in the received wireless signal.
21. The base station of
22. The base station of
23. The base station of
24. The base station of
25. A user equipment comprising:
a memory;
a processor coupled to the memory; and
program code executable on the processor, the program code operable for:
receiving a wireless signal and producing, from an input of the received wireless signal to a detector, a detected signal, wherein the detected signal is an output from the detector;
producing, from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
producing, from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
26. A base station comprising:
a memory;
a processor coupled to the memory; and
program code executable on the processor, the program code operable for:
receiving a wireless signal and producing from an input of the received wireless signal to a detector, a detected signal, wherein the detected signal is an output from the detector;
producing from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
producing from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
27. A computer-readable medium encoded with executable instructions for noise variance estimation of a detected signal, the instructions comprising instructions for:
receiving a wireless signal and producing from an input of the received wireless signal to a detector, a detected signal, wherein the detected signal is an output from the detector;
producing from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
producing from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
28. The computer-readable medium of
applying a function equal to a transfer function of the detector to the first noise variance signal.
29. The computer-readable medium of
30. The computer-readable medium of
31. A communication system configured to provide for noise variance estimation of a detected signal, the communication system comprising:
a detector for receiving a wireless signal and outputting from an input of the received wireless signal, a detected signal;
first noise variance logic for producing, from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
second noise variance logic for producing, from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
32. An integrated circuit for receiving a signal and detecting therein a detected signal, the integrated circuit comprising:
first noise variance logic or producing, from the received wireless signal, a first noise variance signal representative of noise variance in the received wireless signal; and
second noise variance logic for producing, from the detected signal and the first noise variance signal, a second noise variance signal representative of noise variance estimation of the detector in the received signal.
Description This application is U.S. National Stage entry under 35 U.S.C. § 371 of PCT International Application Ser. No. PCT/GB2004/003368 (International Publication No. WO 2005/015790 A1 and titled “Method and arrangement for noise variance and SIR estimation”) filed on Aug. 5, 2004, which claims benefit of UK Patent Application No. GB 0318529.5 (UK Publication No. GB 2 404 882 A and titled “Method and arrangement for noise variance and SIR estimation”) filed on Aug. 7, 2003, both from applicant IPWireless and both of which are incorporated herein by reference in their entirety. This invention relates to noise variance and signal/interference ratio (SIR) estimation, and particularly though not exclusively to such estimation in wireless communication receivers. It will be understood that, as used herein, the terms ‘noise’ and ‘interference’ are to be considered synonymous, with each encompassing both noise and interference. In the field of this invention it is known that many parts of a wireless communications receiver often require an estimation of noise variance and/or SIR. This is needed for purposes of power control, threshold determination for various algorithms, quantisation of soft-decision information for channel decoding purposes to name but a few. For BPSK (Binary Phase Shift Key) and QPSK (Quadrature Phase Shift Key) modulation the conventional method for estimating the SIR at the output of a detector relies on estimating output noise variance using the following equality known (for example) from the publication by Papoulis and Pillai, entitled ‘Probability, Random Variables and Stochastic Processes’, 3rd Ed. 1991,
where {circumflex over (σ)} This yields the following result:
where SIR represents the SIR of the k However, this approach has the disadvantage(s) that the accuracy of this method at low SIR is poor since it suffers from a bias term. An analysis of the bias term and a correction method has been suggested in UK Patent Application GB 0128475.1 (UK Publication No. GB 2 382 748 A and titled “Signal to noise plus interference ration (SNIR) estimation with correction factor” to applicant IPWireless) filed on Nov. 28, 2001. However, the suggested correction method requires a look-up table to correct for the aforementioned problem, and the estimation variance is also increased when correcting the bias. A need therefore exists for a method and arrangement for noise variance and SIR estimation wherein the abovementioned disadvantage(s) may be alleviated. In accordance with embodiments of the present invention there is provided a method for noise variance estimation, user equipment, base station, computer program product, communication system and an integrated circuit as claimed. In some embodiments, the second noise variance signal is produced by applying to the first noise variance signal a function substantially equal to the detector's transfer function. In some embodiments, the first noise variance signal is derived from a midamble portion of the received signal. In some embodiments, an estimate of total power at the detector output is produced from the second noise variance signal and an SIR signal representative of SIR in the received signal. One method and arrangement for noise variance and SIR estimation incorporating the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: The following preferred embodiment of the present invention will be described in the context of a 3GPP (3 In the terminal/user equipment domain Thus, the elements RNC The RNC The SGSN The GGSN Such a UTRAN system and its operation are described more fully in the 3GPP technical specification documents 3GPP TS 25.401, 3GPP TS 23.060, and related documents, available from the 3GPP website, and need not be described in more detail herein. The physical layer of UTRA TDD mode provides physical channels that carry transport channels from the MAC (Medium Access Control) sub-layer of UMTS Layer The data fields contain the data symbols from the transport channels, after the processes of coding, multiplexing, interleaving, and modulation. The midamble field contains the training sequence, which is used in a number of Layer
The received sequence in the data payload areas of the burst is given by
(.)
where b The output of the detector is given by
where f(.) denotes the transfer function of the detector, the vector r contains the desired symbols, and the vector z contains noise plus interference. The average power for the k Expanding p Under the assumption that the noise is uncorrelated with the signal vector r, the average power for the k where E(.) is the statistical average, σ
The conventional method for estimating the SIR relies on estimating the detector output noise variance using the following equality mentioned above:
to yield the following result:
As discussed above, the accuracy of this approach at low SIR is poor since it suffers from a bias term, which may be corrected by use of a look-up table. As will be discussed in greater,detail below, the following preferred embodiments of the present invention do not suffer from such a bias term and therefore do not require a look-up table to correct for the aforementioned problem. Referring now to The estimated output noise variance then allows an improved estimate of the SIR (SIR In the following description, two types of CDMA (Code Division Multiple Access) detector are considered, namely single user detector (SUD) and multiuser detector (MUD). It will be understood that the invention is also applicable to other types of detector such as a RAKE receiver. The technique described here is based on first estimating the noise variance at the input to the detector and then mapping the input noise variance to the output noise variance using the transfer function of the detector. The process of estimating the noise variance at the input to the detector is carried out using the midamble portion of the burst. Considering the received sequence of chip spaced samples e=(e
where where X≦L Multiuser Detection Under the assumption that the noise is white with variance σ where I is the identity matrix and
From equation (2), the noise variance seen at the output of the MUD is given by
where ∥.∥ denotes vector norm, and σ where f({circumflex over (σ)} Using the new estimate for the output noise variance, the SIR at the output of the MUD for the k
where the error term δ({circumflex over (σ)}
It is clear from the above set of equations that when {circumflex over (σ)}
It will therefore be understood that the accuracy of the above technique is directly related to the quality of the noise variance estimate, {circumflex over (σ)} Single User Detection For the single user detector case the received sequence is written as
The matrix H has dimensions (NQ+W−1)×NQ and its elements are given by
where h=(h
For Minimum Mean Squared Error (MMSE) symbol estimation and under the assumption that the noise is white with variance σ From equation (4), the noise variance seen at the output of the SUD is given by
where ∥.∥ denotes vector norm, the multiplier G comes from the matrix C, and in general G=∥c By replacing σ where G is replaced with Q and f({circumflex over (σ)}
where the error term δ({circumflex over (σ)}
It is clear from the above set of equations that when {circumflex over (σ)}
It will therefore be understood that the accuracy of the above technique is directly related to the quality of the noise variance estimate, {circumflex over (σ)} It will be appreciated that the method described above for noise variance and SNIR estimation may be carried out in software running on a processor (not shown—e.g., in User Equipment such as It will be also be appreciated that the arrangement described above for noise variance and SNIR estimation may alternatively be carried out in hardware, for example in the form of an integrated circuit (not shown) such as an FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Integrated Circuit). It will be understood that the method and arrangement for noise variance and SIR estimation described above provides the following advantages that the accuracy of this technique is not poor at low SIR, since it does not suffer from a bias term, nor does it require correction therefor using a look-up table. An additional advantage is that any increase in estimation variance resulting from bias correction may be avoided. Patent Citations
Non-Patent Citations
Referenced by
Classifications
Legal Events
Rotate |